Agricultural combines for harvesting and threshing of crop materials are well known in the art. Typically, agricultural combines includes a crop harvesting apparatus which reaps planted grain stalks, and an infeed mechanism arranged at the forward end of the combine to feed the grain stalks to a separating apparatus. The separating apparatus acts on the crop materials to thresh and separate grain from material other than grain (MOG).
Threshing takes place between an elongated rotor assembly and a cylindrical housing which encases the rotor assembly. The rotor assembly includes a cylindrical rotor drum having a plurality of threshing elements radiating from it. The threshing elements are mounted on the outer skin of the rotor, and may take the form of rasp bars which can be, for example, arranged in a helical path around the rotor, fastened to the outer skin of the rotor on suitably configured brackets.
The separating apparatus typically includes an axially elongated pierced casing or cage surrounding a rotor. Between the upstream and downstream ends of the separating apparatus, the crop materials are repeatedly threshed as the cage spirals around the large diameter rotor. Suitable instrumentalities on the rotor cooperate with an axially elongated threshing section on the lower portion of the casing to thresh the crop materials such that most of the grain will be separated and propelled downwardly through the threshing section. The threshing section of the casing or cage is comprised, at least in part, by a series of side-by-side semi-cylindrical perforated concaves and semi-cylindrical grates. The rotor cooperates with the semicylindrical concaves and semicylindrical grates to thresh the crop materials such that most of the grain will be separated and propelled downwardly through the concaves and grates.
During this process, the primary separation of grain from MOG is provided in the concave area. Here, the crop materials including both grain and MOG are compressed, and then rotated around the cage area, such that the easily-removed grain is threshed from the MOG. The crop material mix progresses to the semicylindrical grate area, where additional threshing is performed to separate additional remaining grain from MOG.
While prior art axial combines have been largely successful in separating grain, a significant portion of grain remains in the crop mix after the grating process. There remains a need, therefore, for an improved threshing system for separating grain from other material.